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We study the influence of the ferrite substrates on the near-field UHF RF identification (RFID) systems by relating their effective permeability μeff to the tag resonance parameters (voltage VIC, center frequency f0) and the system-level performance (reading distance RD). To this effect, a new method to predict the disc μeff is used (fluxmetric approach) with good fit to the measured values. In addition, whereas the magnetic substrate normally yields the decrement of VIC and f0 it also enables the tag downsizing and the RD increase. The conducted RD measurements with planar hexaferrite discs support this theoretical capability. Moreover, further improvement in RD is achieved when the discs are loaded to the reader loop antenna. Our ferrite samples are also found effective in shielding RFID from the metallic environment's implications, yet no discernible difference between permeable and lossy samples is realized. Full understanding of the underlying mechanisms governing the materials-system interaction is thereby provided to the RFID designer.